U.S. patent number 10,983,004 [Application Number 16/383,793] was granted by the patent office on 2021-04-20 for spectrum correction device, spectrum correction method, and non-transitory computer readable storage medium.
This patent grant is currently assigned to Yokogawa Electric Corporation, YOKOGAWA TEST & MEASUREMENT CORPORATION. The grantee listed for this patent is Yokogawa Electric Corporation, Yokogawa Test & Measurement Corporation. Invention is credited to Gentaro Ishihara, Manabu Kojima.
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United States Patent |
10,983,004 |
Ishihara , et al. |
April 20, 2021 |
Spectrum correction device, spectrum correction method, and
non-transitory computer readable storage medium
Abstract
A spectrum correction device includes an analyzer configured to
analyze a shape of an optical spectrum obtained by measuring a
light to be measured using spectrum data representing the optical
spectrum, a corrector configured to perform a correction process
according to the shape of the optical spectrum to the spectrum data
based on an analysis result of the analyzer, and a synthesizer
configured to synthesize the spectrum data corrected by the
corrector.
Inventors: |
Ishihara; Gentaro (Tokyo,
JP), Kojima; Manabu (Tokyo, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Yokogawa Electric Corporation
Yokogawa Test & Measurement Corporation |
Tokyo
Tokyo |
N/A
N/A |
JP
JP |
|
|
Assignee: |
Yokogawa Electric Corporation
(Tokyo, JP)
YOKOGAWA TEST & MEASUREMENT CORPORATION (Tokyo,
JP)
|
Family
ID: |
1000005499918 |
Appl.
No.: |
16/383,793 |
Filed: |
April 15, 2019 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20190323887 A1 |
Oct 24, 2019 |
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Foreign Application Priority Data
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Apr 23, 2018 [JP] |
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JP2018-082650 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01J
3/0297 (20130101); G01J 3/2803 (20130101) |
Current International
Class: |
G01J
3/02 (20060101); G01J 3/28 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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59-013922 |
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Jan 1984 |
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JP |
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2001-099710 |
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Apr 2001 |
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JP |
|
3189162 |
|
Jul 2001 |
|
JP |
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2009-180679 |
|
Aug 2009 |
|
JP |
|
2015-049168 |
|
Mar 2015 |
|
JP |
|
Primary Examiner: Nur; Abdullahi
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
What is claimed is:
1. A spectrum correction device comprising: a hardware processor
configured to execute a program stored in a storage to implement:
an analyzer configured to analyze a shape of an optical spectrum
obtained by measuring a light to be measured using spectrum data
representing the optical spectrum; a corrector configured to
perform a correction process according to the shape of the optical
spectrum to the spectrum data based on an analysis result of the
analyzer; and a synthesizer configured to synthesize the spectrum
data corrected by the corrector, wherein the corrector is
configured to perform the correction process using a correction
method selected from a plurality of correction methods prepared in
advance in accordance with the shape of the optical spectrum based
on the analysis result of the analyzer.
2. The spectrum correction device according to claim 1, wherein a
first correction method for correcting a wavelength resolution of
the optical spectrum and a second correction method for correcting
the shape of the optical spectrum by expanding or contracting the
optical spectrum in a wavelength axis direction or a frequency axis
direction are prepared in the corrector.
3. The spectrum correction device according to claim 2, wherein the
corrector is configured to select the first correction method or
the second correction method to perform the correction process in
accordance with a slope of the optical spectrum analyzed by the
analyzer.
4. The spectrum correction device according to claim 3, wherein the
corrector is configured to select the first correction method to
perform the correction process for a portion where an absolute
value of the slope of the optical spectrum is equal to or less than
a predetermined threshold value, and wherein the corrector is
configured to select the second correction method to perform the
correction process for a portion where the absolute value of the
slope of the optical spectrum is greater than the threshold
value.
5. The spectrum correction device according to claim 4, wherein the
threshold value is set in accordance with characteristics of a
spectroscope used for measurement of the light to be measured.
6. The spectrum correction device according to claim 1, wherein the
corrector is configured to perform the correction process in
accordance with a result of comparison between an absolute value of
the slope of the optical spectrum and a plurality of predetermined
threshold values, using a correction method selected from a
plurality of correction methods prepared in advance in accordance
with the shape of the optical spectrum.
7. The spectrum correction device according to claim 1, wherein the
corrector is configured to perform the correction process using a
correction method selected from a plurality of correction methods
prepared in advance in accordance with an amount of noise
components superposed on the optical spectrum analyzed by the
analyzer.
8. A spectrum correction device comprising: a hardware processor
configured to execute a program stored in a storage to implement:
an analyzer configured to analyze a shape of an optical spectrum
obtained by measuring a light to be measured using spectrum data
representing the optical spectrum; a corrector configured to
perform a correction process according to the shape of the optical
spectrum to the spectrum data based on an analysis result of the
analyzer; and a synthesizer configured to synthesize the spectrum
data corrected by the corrector, wherein the synthesizer is
configured to synthesize the spectrum data corrected by the
corrector so that a discontinuity does not occur in the optical
spectrum after synthesizing.
9. The spectrum correction device according to claim 8, wherein the
synthesizer is configured to process at least a part of the
spectrum data corrected by the corrector in an optical power axis
direction so that the discontinuity does not occur.
10. A spectrum correction method comprising: analyzing, by an
analyzer, a shape of an optical spectrum obtained by measuring a
light to be measured using spectrum data representing the optical
spectrum; performing, by a corrector, a correction process
according to the shape of the optical spectrum to the spectrum data
based on an analysis result of the analyzer; synthesizing, by a
synthesizer, the spectrum data corrected by the corrector; and
performing, by the corrector, the correction process using a
correction method selected from a plurality of correction methods
prepared in advance in accordance with the shape of the optical
spectrum based on the analysis result of the analyzer.
11. The spectrum correction method according to claim 10, wherein a
first correction method for correcting a wavelength resolution of
the optical spectrum and a second correction method for correcting
the shape of the optical spectrum by expanding or contracting the
optical spectrum in a wavelength axis direction or a frequency axis
direction are prepared in the corrector.
12. The spectrum correction method according to claim 11, further
comprising: selecting, by the corrector, the first correction
method or the second correction method to perform the correction
process in accordance with a slope of the optical spectrum analyzed
by the analyzer.
13. The spectrum correction method according to claim 12, further
comprising: selecting, by the corrector, the first correction
method to perform the correction process for a portion where an
absolute value of the slope of the optical spectrum is equal to or
less than a predetermined threshold value; and selecting, by the
corrector, the second correction method to perform the correction
process for a portion where the absolute value of the slope of the
optical spectrum is greater than the threshold value.
14. The spectrum correction method according to claim 13, wherein
the threshold value is set in accordance with characteristics of a
spectroscope used for measurement of the light to be measured.
15. The spectrum correction method according to claim 10, further
comprising: performing, by the corrector, the correction process in
accordance with a result of comparison between an absolute value of
the slope of the optical spectrum and a plurality of predetermined
threshold values, using a correction method selected from a
plurality of correction methods prepared in advance in accordance
with the shape of the optical spectrum.
16. A spectrum correction method comprising: analyzing, by an
analyzer, a shape of an optical spectrum obtained by measuring a
light to be measured using spectrum data representing the optical
spectrum; performing, by a corrector, a correction process
according to the shape of the optical spectrum to the spectrum data
based on an analysis result of the analyzer; synthesizing, by a
synthesizer, the spectrum data corrected by the corrector; and
synthesizing, by the synthesizer, the spectrum data corrected by
the corrector so that a discontinuity does not occur in the optical
spectrum after synthesizing.
17. The spectrum correction method according to claim 16, further
comprising: processing, by the synthesizer, at least a part of the
spectrum data corrected by the corrector in an optical power axis
direction so that the discontinuity does not occur.
18. A non-transitory computer readable storage medium storing one
or more spectrum correction programs configured for execution by a
computer, the one or more spectrum correction programs comprising
instructions for: analyzing, by an analyzer, a shape of an optical
spectrum obtained by measuring a light to be measured using
spectrum data representing the optical spectrum; performing, by a
corrector, a correction process according to the shape of the
optical spectrum to the spectrum data based on an analysis result
of the analyzer; synthesizing, by a synthesizer, the spectrum data
corrected by the corrector; and performing, by the corrector, the
correction process using a correction method selected from a
plurality of correction methods prepared in advance in accordance
with the shape of the optical spectrum based on the analysis result
of the analyzer.
19. A non-transitory computer readable storage medium storing one
or more spectrum correction programs configured for execution by a
computer, the one or more spectrum correction programs comprising
instructions for: analyzing, by an analyzer, a shape of an optical
spectrum obtained by measuring a light to be measured using
spectrum data representing the optical spectrum; performing, by a
corrector, a correction process according to the shape of the
optical spectrum to the spectrum data based on an analysis result
of the analyzer; synthesizing, by a synthesizer, the spectrum data
corrected by the corrector; and synthesizing, by the synthesizer,
the spectrum data corrected by the corrector so that a
discontinuity does not occur in the optical spectrum after
synthesizing.
Description
BACKGROUND
Technical Fields
The present invention relates to a spectrum correction device, a
spectrum correction method and a non-transitory computer readable
storage medium.
Priority is claimed on Japanese Patent Application No. 2018-082650,
filed on Apr. 23, 2018, the contents of which are incorporated
herein by reference.
Related Art
Intensity characteristics (optical spectrum) of light to be
measured for respective wavelengths or frequencies are measured
using an optical spectrum analyzer in many cases. This optical
spectrum analyzer is a device that includes a spectroscope that
disperses light to be measured, a light detector that detects the
light dispersed by the spectroscope and a processing device that
performs signal processing on a detection signal output from the
light detector to obtain an optical spectrum, for example, and
displays a 2-dimensional graph having the horizontal axis
representing wavelength or frequency and the vertical axis
representing intensity (power).
Japanese Patent No. 3189162 discloses an example of a conventional
optical spectrum analyzer. Specifically, an optical spectrum
analyzer that can obtain an accurate optical spectrum in an
arbitrarily determined wavelength bandwidth (wavelength resolution)
even in cases in which the width of an emission slit of a
spectroscope cannot be arbitrarily changed and the like is
disclosed. This optical spectrum analyzer performs a correction
process of simple-moving-averaging (moving adding up) a light
intensity measurement value P(i) at each measurement point i of the
measured optical spectrum in the arbitrarily determined wavelength
bandwidth (wavelength resolution). Since the wavelength resolution
of the spectroscope is corrected by performing such a correction
process, it is possible to obtain an accurate optical spectrum in
an arbitrarily determined wavelength bandwidth (wavelength
resolution).
Incidentally, the aforementioned optical spectrum analyzer
disclosed in Japanese Patent No. 3189162 can obtain an accurate
optical spectrum in an arbitrarily determined wavelength bandwidth
(wavelength resolution) in many cases by performing the
aforementioned correction process. However, there is a problem that
an accurate optical spectrum may not be able to be obtained when
the aforementioned correction process is performed in specific
cases (e.g., a case in which the wavelength bandwidth of light to
be measured is narrower than a measurement wavelength resolution as
in a main mode of a distributed feed-back (DFB) laser).
SUMMARY
To solve these problems, a spectrum correction device according to
one aspect of the present invention may include an analyzer
configured to analyze a shape of an optical spectrum obtained by
measuring a light to be measured using spectrum data representing
the optical spectrum, a corrector configured to perform a
correction process according to the shape of the optical spectrum
to the spectrum data based on an analysis result of the analyzer,
and a synthesizer configured to synthesize the spectrum data
corrected by the corrector.
Further features and aspects of the present disclosure will become
apparent from the following detailed description of exemplary
embodiments with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing main components of an optical spectrum
analyzer including a spectrum correction device according to a
first embodiment of the present invention.
FIG. 2 is a flowchart showing a spectrum correction method
according to the first embodiment of the present invention.
FIG. 3 is a diagram showing an example of an optical spectrum shape
analysis result in the first embodiment of the present
invention.
FIG. 4A is a diagram showing an example of optical spectra on which
a correction process has been performed in the first embodiment of
the present invention.
FIG. 4B is a diagram showing an example of optical spectra on which
a correction process has been performed in the first embodiment of
the present invention.
FIG. 5 is an enlarged diagram of a peak portion of an optical
spectrum shown in FIG. 4B.
FIG. 6A is a diagram showing an example of optical spectra acquired
by a synthesizing process in the first embodiment of the present
invention.
FIG. 6B is a diagram showing an example of optical spectra acquired
by a synthesizing process in the first embodiment of the present
invention.
FIG. 7 is a flowchart showing a spectrum correction method
according to a second embodiment of the present invention.
FIG. 8A is a diagram for describing problem 1 generated in a
conventional optical spectrum analyzer.
FIG. 8B is a diagram for describing problem 1 generated in a
conventional optical spectrum analyzer.
FIG. 9 is a diagram for describing problem 2 generated in the
conventional optical spectrum analyzer.
DETAILED DESCRIPTION OF THE EMBODIMENTS
The embodiments of the present invention will be now described
herein with reference to illustrative preferred embodiments. Those
skilled in the art will recognize that many alternative preferred
embodiments can be accomplished using the teaching of the present
invention and that the present invention is not limited to the
preferred embodiments illustrated herein for explanatory
purposes.
An aspect of the present invention is to provide a spectrum
correction device, a spectrum correction method and a
non-transitory computer readable storage medium capable of
obtaining a more accurate optical spectrum than a conventional
one.
Hereinafter, a spectrum correction device, a spectrum correction
method and a non-transitory computer readable storage medium
according to embodiments of the present invention will be described
with reference to the drawings. In the following, the overview of
the present embodiment will be described first and then each
embodiment will be described in detail.
[Overview]
Embodiments of the present invention allow a more accurate optical
spectrum than a conventional one to be obtained. Specifically,
embodiments of the present invention allow a more accurate optical
spectrum than a conventional one to be obtained by solving the
following two problems generated in a conventional optical spectrum
analyzer when the wavelength bandwidth of light to be measured is
narrower than a measurement wavelength resolution. [Problem 1] The
top portion of peak portions of an optical spectrum after
correction may be rounded and the peak portions may be widened
overall to lead to lack of sharpness in the optical spectrum,
resulting in deterioration in a vicinal dynamic range (capability
of separately measuring other peak portions adjacent to a certain
peak portion of an optical spectrum) of the optical spectrum.
[Problem 2] The peak power of the optical spectrum before
correction differs from that after correction.
FIG. 8A and FIG. 8B are diagrams for describing the problem 1
generated in a conventional optical spectrum analyzer. FIG. 8A is a
diagram enlarging and showing one peak portion of optical spectra
and FIG. 8B is a diagram further enlarging the peak portion shown
in FIG. 8A. Optical spectra SP101 to SP103 shown in FIG. 8A and
FIG. 8B are obtained by measuring a laser beam emitted from a DFB
laser light source having a wavelength of 1548.434 and an optical
power of approximately 10 dBm.
The optical spectrum SP101 is obtained by measuring the laser beam
using a spectroscope having a wavelength resolution set to 0.069
nm. The optical spectrum SP102 is obtained by correcting spectrum
data representing the optical spectrum SP101 using a conventional
technique such that the wavelength resolution becomes 0.1 nm. The
optical spectrum SP103 is acquired by measuring the laser beam
using a spectroscope having a wavelength resolution set to 0.1
nm.
In general, a wavelength resolution of a spectroscope is
represented as a width (full width at half maximum) at a portion 3
dB below a peak (top portion) of an optical spectrum obtained by
measuring a single-wavelength light source. Referring to FIG. 8B
which enlarges a peak portion PK of the optical spectra shown in
FIG. 8A, it can be ascertained that the wavelength resolution of
the optical spectrum SP101 is 0.069 nm that is the same as the
wavelength resolution set in the spectroscope. In addition, it can
be ascertained that the wavelength resolution of the optical
spectrum SP102 is 0.1 nm that is a wavelength resolution which has
been corrected. Further, it can be ascertained that the wavelength
resolution of the optical spectrum SP103 is 0.1 nm that is the same
as the wavelength resolution set in the spectroscope. That is, it
can be ascertained that the wavelength resolution is corrected to a
desired wavelength resolution in the conventional technique with
only the wavelength resolution being involved.
However, referring to the entire peak portion PK of the optical
spectra as shown in FIG. 8A, it can be ascertained that the top
shape of the peak portion PK of the optical spectrum SP102 after
correction is rounded compared to the optical spectrum SP103 that
is not corrected and the peak portion PK is widened overall to lead
to lack of sharpness in the optical spectrum. Furthermore, it can
be ascertained that correction has been correctly performed with
respect to baseline portions BL (low optical power portions between
the peak portion PK and other peak portions that are not shown) of
the optical spectra from the fact that the optical power of the
optical spectrum SP102 after correction is higher than the optical
power of the optical spectrum SP101 before correction by 1.6 dB
(about 45%) and is consistent with a ratio (0.1/0.069=1.449) of
resolution before correction to resolution after correction.
Here, when the top shape of the peak portion PK in the optical
spectra is rounded according to correction and thus a vicinal
dynamic range of the optical spectra deteriorates, separate
measurement of each laser beam may become unclear when optical
spectra of a plurality of laser beams having adjacent wavelengths
are measured. For example, when wavelength division multiplexing
(WDM) signal light in which a plurality of laser beams having
different wavelengths have been multiplexed is measured, a
measurement wavelength resolution is set to be narrower than the
wavelength interval of the WDM signal light such that a signal
optical spectrum of each wavelength can be separately measured.
However, when the vicinal dynamic range deteriorates, the optical
spectrum of each laser beam may not be clearly separated.
FIG. 9 is a diagram for describing problem 2 generated in the
conventional optical spectrum analyzer. Further, optical spectra
SP101 and SP102 shown in FIG. 9 are obtained by enlarging the peak
portions PK of the optical spectral SP101 and SP102 shown in FIG.
8. Referring to FIG. 9, it can be ascertained that the peak power
of the optical spectrum SP102 after correction decreases by about
0.04 dB (about 0.9%) compared to the peak power of the optical
spectrum SP101 before correction.
The aforementioned problems 1 and 2 are generated because spectrum
data representing an optical spectrum is simple-moving-averaged in
a wavelength width direction in an arbitrarily determined
wavelength bandwidth (wavelength resolution) in the conventional
technique. In embodiments of the present invention, a more accurate
optical spectrum than a conventional one is obtained by minimizing
change in shape (rounding and widening) of a peak portion PK of an
optical spectrum after correction and causing the peak power of the
optical spectrum before correction to be the same as that after
correction.
First Embodiment
FIG. 1 is a diagram showing main components of an optical spectrum
analyzer including a spectrum correction device according to a
first embodiment of the present invention. As shown in FIG. 1, the
optical spectrum analyzer 1 includes a spectroscope 11, a light
detector 12, an amplifier 13, an A/D converter 14, and a signal
processing device 15 (spectrum correction device) and performs
processes of measuring optical spectra of light L to be measured
input through an optical fiber which is not shown, for example, and
correcting the measured optical spectra.
The spectroscope 11 disperses the input light L to be measured and
outputs desired wavelength components among wavelength components
included in the light L to be measured. For example, the
spectroscope 11 operates to sequentially output wavelength
components in a wavelength range set in advance among the
wavelength components included in the light L to be measured. The
light detector 12 detects the wavelength components output from the
spectroscope 11 and outputs a signal (analog signal) indicating an
optical power (intensity) of the detected wavelength components. As
this light detector 12, for example, a photodiode can be used. The
amplifier 13 amplifies the signal output from the light detector 12
with a prescribed amplification factor. The A/D converter 14
converts the signal (analog signal) amplified by the amplifier 13
into a digital signal and outputs the digital signal to the signal
processing device 15.
The signal processing device 15 includes a storage 21, an operation
device 22, a display 23 and a signal processor 24 connected to a
bus B. The storage 21 stores various types of data, various
parameters and various programs used in the signal processing
device 15. For example, the storage 21 stores a digital signal
(spectrum data) output from the A/D converter 14 and input through
the bus B. In addition, the storage 21 stores programs for
realizing functions (an analyzer 24a, a corrector 24b, a
synthesizer 24c, and the like which will be described later) of the
signal processor 24, for example. The storage 21 is composed of a
hard disk drive (HDD), a solid state drive (SSD), a random access
memory (RAM), a read only memory (ROM), or the like and performs
input/output of various types of information under the control of
the signal processor 24.
The operation device 22 includes various operation buttons such as
function keys and numerical keys and a touch panel and outputs an
instruction according to an operation of a user who uses the
optical spectrum analyzer 1 to the signal processor 24. The display
23 includes a display device, for example, a liquid crystal display
(LCD), a cathode ray tube (CRT) or the like, and displays various
types of information output from the signal processor 24. For
example, the display 23 displays an optical spectrum obtained by
visualizing spectrum data. Meanwhile, the operation device 22 and
the display 23 may be physically separated or may be physically
integrated like in a touch panel type liquid crystal display having
both a display function and an operation function.
The signal processor 24 generally controls operations of the
optical spectrum analyzer 1 and performs various types of signal
processing. For example, the signal processor 24 reads spectrum
data stored in the storage 21 and performs signal processing for
obtaining optical spectra of the light L to be measured. In
addition, the signal processor 24 includes the analyzer 24a
(analysis means), the corrector 24b (correction means), and a
synthesizer 24c (synthesizing means) and performs signal processing
for correcting optical spectra based on an instruction output from
the operation device 22, for example.
The analyzer 24a performs an analysis process of analyzing shapes
of optical spectra obtained by measuring the light L to be measured
using spectrum data read from the storage 21, for example. The
analyzer 24a performs a process of obtaining a slope in each
wavelength of the spectrum data, a process of obtaining an
inflection point of a slope of the spectrum data, a process of
obtaining the amount of noise components superposed on the spectrum
data, and other processes, for example, as the analysis
process.
Here, spectrum data at a measurement point i (i is an integer equal
to or larger than 1) is represented as P(i). Further, the unit of
the spectrum data P(i) is W or dBm. In addition, a measurement
wavelength resolution at the measurement point i of the spectrum
data P(i) is represented as RB(i). The measurement wavelength
resolution RB(i) indicates the wavelength resolution of the
spectroscope 11 and is provided by being calculated in advance or
defined as a constant. Further, the unit of the measurement
wavelength resolution RB(i) is m. The analyzer 24a obtains an
amount of change (slope amount S(i)) in optical power (optical
intensity) per measurement wavelength resolution RB(i) of the
spectrum data P(i) as the aforementioned slope, for example.
Further, the unit of the slope amount S(i) is dB/RES.
The corrector 24b performs a correction process according to the
shape of an optical spectrum to the spectrum data based on an
analysis result of the analyzer 24a. Specifically, the corrector
24b performs the aforementioned correction process using a
correction method selected from a plurality of correction methods
prepared in advance in accordance with the shape of an optical
spectrum based on an analysis result of the analyzer 24a. For
example, a wavelength resolution correction method (first
correction method) for correcting a wavelength resolution of an
optical spectrum and a shape correction method (second correction
method) for correcting the shape of an optical spectrum by
expanding or contracting the optical spectrum in a wavelength axis
direction or a frequency axis direction may be prepared in the
corrector 24b, and the corrector 24b may select the wavelength
resolution correction method or the shape correction method in
accordance with slopes of optical spectra determined by the
analyzer 24a to perform the aforementioned correction process.
Here, the corrector 24b may select the wavelength resolution
correction method or the shape correction method using a threshold
value Sth set in accordance with characteristics of the
spectroscope 11 used for measurement of the light L to be measured
in selection of the wavelength resolution correction method or the
shape correction method. For example, the wavelength resolution
correction method may be selected to perform the correction process
for a portion where the absolute value of a slope of an optical
spectrum is equal to or less than the threshold value Sth and the
shape correction method may be selected to perform the correction
process for a portion where the absolute value of the slope of the
optical spectrum is greater than the threshold value Sth.
The synthesizer 24c synthesizes spectrum data corrected by the
corrector 24b.
Specifically, the synthesizer 24c synthesizes the spectrum data
corrected by the corrector 24b such that a discontinuity does not
occur in a synthesized optical spectrum. For example, the
synthesizer 24c may process the spectrum data corrected by the
corrector 24b partially in an optical power axis direction such
that a discontinuity does not occur.
Functions (the analyzer 24a, the corrector 24b and the synthesizer
24c) of the signal processor 24 are realized as software by
executing programs stored in the storage 21. That is, each function
of the signal processor 24 is realized by software and hardware
resources in cooperation. Further, a program for realizing each
function of the signal processor 24 may be distributed in a state
in which it has been recorded in a computer readable recording
medium such as a CD-ROM, DVD (registered trademark)-ROM or a
universal serial bus (USB) memory or may be distributed through a
network such as the Internet.
FIG. 2 is a flowchart showing a spectrum correction method
according to the first embodiment of the present invention. The
flowchart shown in FIG. 2 starts when a spectrum correction
instruction is issued according to a user operation through the
operation device 22 or when new spectrum data has been acquired
through optical spectrum measurement in a state in which execution
of spectrum correction has been set in advance, for example.
When the procedure of the flowchart shown in FIG. 2 starts, the
signal processor 24 performs a process of inputting spectrum data
P(i) (step S11). For example, the signal processor 24 performs a
process of reading the spectrum data P(i) stored in the storage 21
and inputting the spectrum data P(i) to the analyzer 24a.
Meanwhile, the number of pieces of spectrum data P(i) (the number
of pieces of data) input in this process is about hundreds to tens
of thousands, for example. Subsequently, the analyzer 24a performs
a process of analyzing shapes of optical spectra using the spectrum
data P(i) input in step S11 (step S12: analysis step).
For example, the analyzer 24a performs a process of obtaining a
slope amount S(i) that is an amount of change in optical power per
measurement wavelength resolution RB(i) of the spectrum data P(i).
Further, the analyzer 24a may perform a process of obtaining an
inflection point of a slope of the spectrum data P(i) and a process
of obtaining an amount of noise components superposed on the
spectrum data P(i) along with or instead of the process of
obtaining the slope amount S(i).
FIG. 3 is a diagram showing an example of an optical spectrum shape
analysis result in the first embodiment of the present invention.
An optical spectrum SP1 shown in FIG. 3 is obtained by measuring a
laser beam emitted from a DFB laser light source having a
wavelength of 1548.434 nm and optical power of about 10 dBm using
the spectroscope 11 having a wavelength resolution set to 0.069 nm.
Further, the optical spectrum SP1 is the same as the optical
spectrum SP101 shown in FIG. 8A.
A slope SL shown in FIG. 3 indicates the slope amount S(i) of the
optical spectrum SP1. Referring to FIG. 3, it can be ascertained
that the absolute value of the slope of the optical spectrum SP1 is
equal to or less than approximately 5 dB/RES with respect to
baseline portions BL of the optical spectrum SP1. On the other
hand, it can be ascertained that the absolute value of the slope of
the optical spectrum SP1 exceeds about 5 dB/RES with respect to a
peak portion PK of the optical spectrum SP1 and may exceed 40
dB/RES. In addition, it can be ascertained that there is a portion
where the sign (positive or negative) of a slope of the optical
spectrum SP1 is reversed in the peak portion PK of the optical
spectrum SP1.
Further, a gentle slope portion (for example, the base line portion
BL) of the optical spectrum SP1 is an optical spectrum of light
having a wider wavelength bandwidth than the wavelength resolution
of the spectroscope 11. On the other hand, a steep slope portion
(for example, the peak portion PK) of the optical spectrum SP1 is
an optical spectrum of light having a narrower wavelength bandwidth
than the wavelength resolution of the spectroscope 11. In this
manner, it is possible to determine whether the wavelength
bandwidth of light to be measured is wider or narrower than the
wavelength resolution of the spectroscope 11 from the slope of the
optical spectrum SP1 for each portion of the optical spectrum
SP1.
Subsequently, the corrector 24b performs a process of selecting a
correction method in accordance with spectrum shape analysis
results (step S13). For example, the corrector 24b performs a
process of comparing a slope amount S(i) at each measurement point
i with the threshold value Sth (threshold value set in accordance
with characteristics of the spectroscope 11 used for measurement of
the light L to be measured) and selecting a correction method
described below according to the comparison result.
When S(i).ltoreq.Sth:
the wavelength resolution correction method for correcting the
wavelength resolution of the optical spectrum SP1 is selected.
When Sth<S(i):
the shape selection method for correcting the shape of the optical
spectrum SP1 is selected.
Subsequently, the corrector 24b performs a process of correcting
the wavelength resolution for a portion of the optical spectrum SP1
for which the wavelength resolution correction method has been
selected (step S14: correction step). On the other hand, the
corrector 24b performs a process of correcting the shape of the
optical spectrum SP1 by expanding or contracting the optical
spectrum SP1 in the wavelength axis direction for a portion of the
optical spectrum SP1 for which the shape correction method has been
selected (step S15: correction step).
FIG. 4A and FIG. 4B are diagrams showing an example of optical
spectra on which a correction process has been performed in the
first embodiment of the present invention. FIG. 4A is a diagram
showing optical spectra before and after correction using the
wavelength resolution correction method, a light section SP1 is an
optical spectrum before correction and an optical spectrum SP2 is
an optical spectrum after correction. In the example shown in FIG.
4A, the wavelength resolution (measurement wavelength resolution
RB(i)) of the optical spectrum SP1 before correction is set to
0.069 nm. Correction using the wavelength resolution correction
method is performed to the optical spectrum SP2 after correction
such that the wavelength resolution R thereof becomes 0.1 nm.
The optical spectra SP1 and SP2 shown in FIG. 4A are the same as
the optical spectra SP101 and SP102 shown in FIG. A. Accordingly,
with respect to the baseline portions BL of the optical spectrum
SP2, the optical power of the optical spectrum SP2 after correction
is higher than the optical power of the optical spectrum SP1 before
correction by 1.6 dB approximately, and correction has been
correctly performed. On the other hand, with respect to the peak
portion PK of the optical spectrum SP2, the top shape is rounded
and widened overall to lead to lack of optical spectrum
sharpness.
FIG. 4B is a diagram showing optical spectra before and after
correction according to the shape correction method, an optical
spectrum SP1 is an optical spectrum before correction and an
optical spectrum SP3 is an optical spectrum after correction. In
the example shown in FIG. 4B, the wavelength resolution
(measurement wavelength resolution RB(i)) of the optical spectrum
SP1 before correction is set to 0.069 nm. Correction using the
shape correction method is performed to the optical spectrum SP3
after correction such that the wavelength resolution R thereof
becomes 0.1 nm. Specifically, shape correction for widening the
width of the peak portion PK of the optical spectrum SP1 before
correction by a difference between the wavelength resolution
(measurement wavelength resolution RB(i)) of the optical spectrum
SP1 before correction and the wavelength resolution R of the
optical spectrum SP3 after correction is performed.
FIG. 5 is an enlarged diagram of the peak portion of the optical
spectrum shown in FIG. 4B. To correct the optical spectrum SP1
having the measurement wavelength resolution RB(i) set to 0.069 nm
such that the wavelength resolution R becomes 0.1 nm, it is
necessary to widen the overall width by 0.031 nm. Accordingly, it
is possible to obtain the optical spectrum SP3 having a wavelength
resolution R of 0.1 nm by equally widening a short-wavelength side
and a long-wavelength side of the peak portion PK by 0.0155 nm.
Here, a method of widening the optical spectrum SP1 may be equally
widening the short-wavelength side and the long-wavelength side of
the peak portion PK, as described above, or weighting any one of
the short-wavelength side and the long-wavelength side of the peak
portion PK and widening the short-wavelength side and the
long-wavelength side of the peak portion PK. For example, when the
measurement wavelength resolution RB(i) of the spectroscope 11 has
wavelength dependency, it is desirable to weight any one of the
short-wavelength side and the long-wavelength side of the peak
portion PK and widen the short-wavelength side and the
long-wavelength side of the peak portion PK in consideration of the
wavelength dependency.
For example, cases in which a measurement wavelength resolution
RB(i) in a main mode has the following wavelength dependency are
conceived.
Measurement wavelength resolution having a center wavelength of
1548.434 nm: 0.069 nm
Measurement wavelength resolution having a wavelength of 1548.384
nm on a short-wavelength side: 0.070 nm
Measurement wavelength resolution having a wavelength of 1548.484
nm on a long-wavelength side: 0.068 nm
In this example, since the long-wavelength side has a narrower
(higher) measurement wavelength resolution than the
short-wavelength side, weighting applied to a widening range is
increased by the difference therebetween. For example, weighting
may be applied to the long-wavelength side in such a manner that
the short-wavelength side becomes 0.015 nm and the long-wavelength
side becomes 0.016 nm to widen the overall width by 0.031 nm
approximately.
Referring to FIG. 5, it can be ascertained that the peak portion PK
of the optical spectrum SP3 has a wavelength resolution of 0.1 nm
and the top shape is not rounded. In addition, since the optical
spectrum SP1 is expanded in the wavelength axis direction but is
not expanded in the optical power axis direction in the shape
correction method, the peak power of the optical spectrum SP3 after
correction is the same as that before correction. Accordingly, a
correct peak power is obtained. On the other hand, the optical
power is not corrected in the baseline portions BL of the optical
spectrum SP3, as shown in FIG. 4B, and thus a correct optical power
is not obtained.
When the above process ends, the synthesizer 24c performs a process
of synthesizing the optical spectrum SP2 corrected in step S14 and
the optical spectrum SP3 corrected in step S15 (step S16:
synthesizing step). For example, the synthesizer 24c performs a
process of synthesizing the optical spectrum SP2 corrected in step
S14 and the optical spectrum SP3 corrected in step S15 such that a
discontinuity does not occur in a synthesized optical spectrum.
FIG. 6A and FIG. 6B are diagrams showing an example of optical
spectra acquired by a synthesizing process in the first embodiment
of the present invention. As shown in FIG. 6A, the baseline
portions BL of the optical spectrum SP2 corrected in step S14
(refer to FIG. 4A) and the peak portion PK of the optical spectrum
SP3 corrected in step S15 (refer to FIG. 4B) are synthesized to
obtain an optical spectrum SP10. Meanwhile, the baseline portions
BL of the optical spectrum SP2 are an optical spectrum of light
(broad-band light) having a wider wavelength bandwidth than the
wavelength resolution of the spectroscope 11, and the peak portion
PK of the optical spectrum SP3 is an optical spectrum of light
(narrow-band light) having a narrower wavelength bandwidth than the
wavelength resolution of the spectroscope 11.
Referring to FIG. 6A, the synthesized optical spectrum SP10 has the
following characteristics. With respect to the baseline portions BL
(portion of broad-band light), the optical power is corrected by a
widened portion of the wavelength resolution to increase by 1.6 dB
approximately. With respect to the peak portion PK (portion of
narrow-band light), the shape of the spectrum is corrected such
that the wavelength resolution becomes 0.1 nm and the peak power is
corrected such that the top portion is not rounded and the peak
power is not changed from the peak power before correction.
Here, the optical spectrum SP10 shown in FIG. 6A is obtained by
synthesizing the baseline portions BL (portion of broad-band light)
and the peak portion PK (portion of narrow-band light) without
performing a special process on the boundaries between the baseline
portions BL and the peak portion PK. That is, the optical spectrum
SP10 is obtained by synthesizing the optical spectra SP2 and SP3
corrected by different correction methods on a short-wavelength
side and a long-wavelength side of the boundaries, and thus a
discontinuity occurs at the boundary portions and stepped portions
appear, as shown in FIG. 6A.
To remove such stepped portions, spectrum data of a portion of
narrow-band light may be processed in the optical power axis
direction. Here, a method of contracting the spectrum data of the
portion of narrow-band light in the optical power axis direction
may be conceived such that the peak power is not changed and the
optical power is consistent at the boundaries between portions of
broad-band light and portions of narrow-band light. Meanwhile, a
slope of an optical spectrum in a portion of narrow-band light is
appearance of characteristics of the spectroscope 11 and does not
represent an actual slope of the optical spectrum of the light L to
be measured. Accordingly, even when spectrum data of a portion of
narrow-band light is contracted in the optical power axis
direction, measurement results do not have an error. By performing
such a process, it is possible to remove a stepped portion at the
boundary between a portion of broad-band light and a portion of
narrow-band light without affecting the peak power of the optical
spectrum SP10, as shown in FIG. 6B.
When the above process ends, the signal processor 24 performs a
process of outputting corrected spectrum data P1(i) (step S17). For
example, the signal processor 24 performs a process of storing the
corrected spectrum data P1(i) in the storage 21 or displaying the
corrected spectrum data P1(i) through the display 23 as a
two-dimensional graph. A series of processes shown in FIG. 2 ends
through the above-described procedure.
As described above, in the present embodiment, the shape of an
optical spectrum is analyzed using spectrum data obtained by
measuring the light L to be measured, a correction process (a
correction process using the wavelength resolution correction
method or a correction process using the shape correction method)
in accordance with the shape of the optical spectrum is performed
to the spectrum data based on the analysis result, and corrected
spectrum data is synthesized. Accordingly, it is possible to
minimize change in shape (rounding or widening) of the peak portion
PK of the corrected optical spectrum. As effects, a vicinal dynamic
range of the optical spectrum (capability of separately measuring
other peak portions adjacent to a certain peak portion of the
optical spectrum) can be prevented from deteriorating. Further, the
peak power of the optical spectrum before correction can be
consistent with that after correction. Accordingly, it is possible
to obtain a more accurate optical spectrum than conventional
ones.
Second Embodiment
FIG. 7 is a flowchart showing a spectrum correction method
according to a second embodiment of the present invention. In FIG.
7, steps in which the same processes as those shown in FIG. 2 are
performed are represented by the same signs.
The spectrum correction method according to the present embodiment
mainly differs from the above-described spectrum correction method
according to the first embodiment in that several correction
methods for correcting spectrum data are added.
Specifically, the flowchart shown in FIG. 7 differs from the
flowchart shown in FIG. 2 in that steps S21 and S22 are provided
instead of steps S12 and S13 in FIG. 2 and new steps S23 and S24
are added. Although approximately the same processes as steps S12
and S13 in FIG. 2 are performed in steps S21 and S22, processes
different from steps S12 and S13 in FIG. 2 are also performed by
adding several correction methods for correcting spectrum data.
Processes performed in steps S21 and S22 will be described in
detail later.
In step S23, a process is performed using the wavelength resolution
correction method for correcting the wavelength resolution of an
optical spectrum as in step S14. However, a correction process
using simple moving averaging is performed in step S14, whereas a
correction process using weighted moving averaging of applying
different weights to pieces of spectrum data P(i) and averaging the
weighted pieces of spectrum data is performed in step S23.
Meanwhile, a method of applying weights to the spectrum data P(i)
is arbitrary. Further, step S24 is a step without correction (in
which a correction process is omitted).
Furthermore, the spectrum correction method according to the
present embodiment includes several correction methods for
correcting spectrum data added to the spectrum correction method
according to the first embodiment, as described above. Accordingly,
the spectrum correction method according to the present embodiment
is performed using a spectrum analyzer having the same
configuration as that of the optical spectrum analyzer 1 shown in
FIG. 1.
When the procedure of the flowchart shown in FIG. 7 starts, first,
the signal processor 24 performs a process of inputting spectrum
data P(i) as in the first embodiment (step S11). Then, the analyzer
24a performs a process of analyzing the shape of an optical
spectrum using the spectrum data P(i) input in step S11 (step S21:
analysis step).
Here, a process of obtaining the amount of noise components in each
wavelength superposed on the spectrum data P(i) is performed in
addition to the process of obtaining a slope amount S(i) that is a
change amount of optical power per measurement wavelength
resolution RB(i) of the spectrum data P(i), for example. As a
method of obtaining the amount of noise components, for example, a
method of obtaining a standard deviation (variation) per
measurement wavelength resolution RB(i) of the spectrum data P(i)
as the amount of noise components can be conceived.
Subsequently, the corrector 24b performs a process of selecting a
correction method in accordance with spectrum shape analysis
results (step S22). For example, the corrector 24b performs a
process of comparing the amount of noise components at each
measurement point i with a predetermined threshold value Nth and
selecting no correction for a portion at which the amount of noise
components exceeds the threshold value Nth. Selection of no
correction is for the purpose of preventing a correction process
from being performed to a portion having many noises to cause an
unnatural optical spectrum.
In addition, for example, the corrector 24b performs a process of
comparing the slope amount S(i) at each measurement point i with a
plurality of threshold values Sth1 and Sth2 (threshold values set
in accordance with characteristics of the spectroscope 11 used for
measurement of the light L to be measured) and selecting a
correction method described below according to the comparison
result. For example, the threshold value Sth1 can be set to 5
dB/RES, and the threshold value Sth2 can be set to 10 dB/RES. In
this manner, it is possible to perform spectrum data wavelength
resolution correction using the plurality of threshold values Sth1
and Sth2 more flexibly compared to the first embodiment.
When S(i).ltoreq.Sth1:
a wavelength resolution correction method using simple moving
averaging is selected.
When Sth1<S(i).ltoreq.Sth2:
a wavelength resolution correction method using weighted moving
averaging is selected.
When Sth2<S(i):
the shape correction method is selected.
Subsequently, the corrector 24b performs a process of correcting a
wavelength resolution through simple moving averaging for a portion
of the optical spectrum SP1 for which the wavelength resolution
correction method using simple moving averaging has been selected
(step S14: correction step). In addition, the corrector 24b
performs a process of correcting a wavelength resolution through
weighted moving averaging for a portion of the optical spectrum SP1
for which the wavelength resolution correction method using
weighted moving averaging has been selected (step S23: correction
step). Further, the corrector 24b performs a process of correcting
the shape of the optical spectrum SP1 by expanding or subtracting
the optical spectrum SP1 in the wavelength axis direction for a
portion of the optical spectrum SP1 for which the shape correction
method has been selected (step S15: correction step). Further, the
corrector 24b does not perform a correction process for a portion
of the optical spectrum SP1 for which no correction has been
selected (step S24).
When the above process ends, the synthesizer 24c performs a process
of synthesizing optical spectra that are not corrected in step S24
in addition to optical spectra corrected in steps S14, S15 and S23
S15 (step S16: synthesizing step). Further, it is also desirable to
synthesize the aforementioned optical spectra such that a
discontinuity does not occur in synthesized optical spectra in the
present embodiment.
When the above process ends, the signal processor 24 performs a
process of outputting corrected spectrum data P1(i) (step S17). For
example, the signal processor 24 performs a process of storing the
corrected spectrum data P1(i) in the storage 21 or displaying the
corrected spectrum data P1(i) through the display 23 as a
two-dimensional graph. A series of processes shown in FIG. 7 ends
through the above-described procedure.
As described above, in the present embodiment, the shape of an
optical spectrum is analyzed using spectrum data obtained by
measuring the light L to be measured, a correction process (a
correction process using the wavelength resolution correction
method according to simple moving averaging, a correction process
using the wavelength resolution correction method according to
weighted moving averaging, or a correction process using the shape
correction method) in accordance with the shape of the optical
spectrum is performed to the spectrum data based on the analysis
result, and corrected spectrum data is synthesized. Accordingly, it
is possible to minimize change in shape (rounding or widening) of
the peak portion PK of the corrected optical spectrum. As effects,
a vicinal dynamic range of the optical spectrum (capability of
separately measuring other peak portions adjacent to a certain peak
portion of the optical spectrum) can be prevented from
deteriorating. Further, the peak power of the optical spectrum
before correction can be consistent with that after correction.
Accordingly, it is possible to obtain a more accurate optical
spectrum than conventional ones.
Although the spectrum correction device, the spectrum correction
method and the spectrum correction program according to embodiments
of the present invention have been described, the present invention
is not limited to the above-described embodiments and can be freely
modified within the scope of the present invention. For example,
although the signal processing device 15 is embedded in the optical
spectrum analyzer 1 as a spectrum correction device in the
above-described embodiments, the signal processing device 15 may be
configured as a separate device that can communicate with the
optical spectrum analyzer 1. For example, the signal processing
device 15 and the optical spectrum analyzer 1 may communicate with
each other through the Internet.
In the spectrum correction device according to one aspect of the
present invention, the corrector performs the correction process
using a correction method selected from a plurality of correction
methods prepared in advance in accordance with the shape of the
optical spectrum based on the analysis result of the analyzer.
Further, in the spectrum correction device according to one aspect
of the present invention, a first correction method for correcting
a wavelength resolution of the optical spectrum and a second
correction method for correcting the shape of the optical spectrum
by expanding or contracting the optical spectrum in a wavelength
axis direction or a frequency axis direction are prepared in the
corrector.
Further, in the spectrum correction device according to one aspect
of the present invention, the corrector selects the first
correction method or the second correction method to perform the
correction process in accordance with a slope of the optical
spectrum analyzed by the analyzer.
Further, in the spectrum correction device according to one aspect
of the present invention, the corrector selects the first
correction method to perform the correction process for a portion
where the absolute value of the slope of the optical spectrum is
equal to or less than a predetermined threshold value Sth, and the
corrector selects the second correction method to perform the
correction process for a portion where the absolute value of the
slope of the optical spectrum is greater than the threshold
value.
Further, in the spectrum correction device according to one aspect
of the present invention, the corrector performs the correction
process in accordance with a result of comparison between an
absolute value of the slope of the optical spectrum and a plurality
of predetermined threshold values Sth1 and Sth2, using a correction
method selected from a plurality of correction methods prepared in
advance in accordance with the shape of the optical spectrum.
Further, in the spectrum correction device according to one aspect
of the present invention, the threshold value is set in accordance
with characteristics of a spectroscope used for measurement of the
light to be measured.
Further, in the spectrum correction device according to one aspect
of the present invention, the synthesizer synthesizes the spectrum
data corrected by the corrector so that a discontinuity does not
occur in the optical spectrum after synthesizing.
Further, in the spectrum correction device according to one aspect
of the present invention, the synthesizer processes at least a part
of the spectrum data corrected by the corrector in an optical power
axis direction so that the discontinuity does not occur.
Further, in the spectrum correction device according to one aspect
of the present invention, the corrector performs the correction
process using a correction method selected from a plurality of
correction methods prepared in advance in accordance with an amount
of noise components superposed on the optical spectrum analyzed by
the analyzer.
A spectrum correction method according to one aspect of the present
invention includes an analysis step S12 and S21 of analyzing a
shape of an optical spectrum obtained by measuring a light L to be
measured using spectrum data representing the optical spectrum, a
correction step S14, S15 and S23 of performing a correction process
according to the shape of the optical spectrum to the spectrum data
based on an analysis result of the analysis step, and a
synthesizing step S16 of synthesizing the spectrum data corrected
in the correction step.
A spectrum correction program according to one aspect of the
present invention causes a computer to function as an analysis
means 24a for analyzing a shape of an optical spectrum obtained by
measuring a light L to be measured using spectrum data representing
the optical spectrum, a correction means 24b for performing a
correction process according to the shape of the optical spectrum
on the spectrum data based on an analysis result of the analysis
means, and a synthesizing means 24c for synthesizing the spectrum
data corrected by the correction means.
As used herein, the following directional terms "front, back,
above, downward, right, left, vertical, horizontal, below,
transverse, row and column" as well as any other similar
directional terms refer to those instructions of a device equipped
with the present invention. Accordingly, these terms, as utilized
to describe the present invention should be interpreted relative to
a device equipped with the present invention.
The term "configured" is used to describe a component, unit or part
of a device includes hardware and/or software that is constructed
and/or programmed to carry out the desired function.
Moreover, terms that are expressed as "means-plus function" in the
claims should include any structure that can be utilized to carry
out the function of that part of the present invention.
The term "unit" is used to describe a component, unit or part of a
hardware and/or software that is constructed and/or programmed to
carry out the desired function. Typical examples of the hardware
may include, but are not limited to, a device and a circuit.
While preferred embodiments of the present invention have been
described and illustrated above, it should be understood that these
are examples of the present invention and are not to be considered
as limiting. Additions, omissions, substitutions, and other
modifications can be made without departing from the scope of the
present invention. Accordingly, the present invention is not to be
considered as being limited by the foregoing description, and is
only limited by the scope of the claims.
* * * * *